PROJECT SUMMARY The use of emerging tobacco products is gaining popularity among youth. Among U.S. high school students, current use of e-cigarettes has outpaced the use of traditional cigarettes. E-cigarettes contain varying levels of nicotine and a number of potentially toxic substances and youth use of e-cigarettes might serve as a gateway for future cigarette use. Cigars currently rank third among the tobacco products most commonly used by youth and also pose serious threats to health; cigar smoke is possibly more toxic than cigarette smoke. The recently finalized ?Deeming Rule? from the Food and Drug Administration (FDA) expanded the agency's regulatory authority over tobacco to include e-cigarettes, cigars, and other newly deemed tobacco products. The first round of new requirements on ?retailer environment? for ?covered tobacco products,? including mandatory age and photo ID checks to prevent illegal sale of these products to minors, was implemented on August 8, 2016. Early studies that were primarily based on community data have shown mixed results regarding the effectiveness of youth access laws to reduce youth cigarette smoking. Recent studies using national probability samples have shown that retail compliance of underage sales laws and restricting tobacco sales to minors are important tobacco prevention strategies. Over the decades, the prevalence of youth cigarette smoking and youth commercial access to cigarettes has been significantly reduced. Despite this progress, the tobacco industry has been promoting alternative tobacco products, such as e-cigarettes, cigars, to entice a new generation of users. The overarching goal of this study is to conduct a quasi-experimental design to assess the impacts of the FDA retail compliance inspections on youth cigar and e-cigarette use behaviors (e.g., ever, current, and frequency of use). This study is innovative in its focus on developing propensity models to predict the violation rate for underage retail sales of e-cigarettes and cigars at the zip code level, and on linking the compliance inspection data with multiple years of national youth survey data in order to assess the potential impacts of regulatory actions. This research will address two of the FDA Center for Tobacco Products (CTP) scientific interest areas: #4 (behavior) and #7 (impact analysis). Results from this study are expected to inform appropriate retail compliance inspection strategies and further expand our knowledge of the potential impacts of regulatory actions on youth e-cigarette and cigar use behaviors.